#include<iostream>

using namespace std;


 struct ListNode {
      int val;
      ListNode *next;
      ListNode() : val(0), next(nullptr) {}
      ListNode(int x) : val(x), next(nullptr) {}
      ListNode(int x, ListNode *next) : val(x), next(next) {}
  };

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if (head == nullptr || head->next == nullptr)
        {
            return head;
        }
        ListNode* newhead = new ListNode(0);
        newhead->next = head;
        ListNode* prev = newhead, * cur = head, * next = cur->next, * nnext = next->next;
        while (cur && next)
        {
            prev->next = next;
            next->next = cur;
            cur->next = nnext;


            prev = cur;
            cur = nnext;
            if (cur)
            {
                next = cur->next;
            }
            if (next)
            {
                nnext = next->next;
            }
        }

        cur = newhead->next;
        delete newhead;
        return cur;
    }
};

int main()
{
    return 0;
}